Monoamine oxidase interactions

Levodopa interacts with many different drugs. When levodopa is used with phenytoin, reserpine, and papaverine, there is a decrease in response to levodopa The risk of a hypertensive crisis increases when levodopa is used with the monoamine oxidase inhibitors (see Chap. 31). Foods high in pyridoxine (vitamin B6) or vitamin B6 preparations reverse the effect of levodopa However, when carbidopa is used with levodopa, pyridoxine has no effect on the action of levodopa hi fact, when levodopa and carbidopa are given together, pyridoxine may be prescribed to decrease the adverse effects associated with levodopa... 

The hypotensive effects of most antihypertensive dru are increased when administered with diuretics and other antihypertensives. Many dnigp can interact with the antihypertensive drugs and decrease their effectiveness (eg, antidepressants, monoamine oxidase inhibitors, antihistamines, and sympathomimetic bronchodilators). When the ACE inhibitors are administered with the NSAIDs, their antihypertensive effect may be decreased. Absorption of the ACE inhibitors may be decreased when administered with the antacids. Administration of potassium-sparing diuretics or potassium supplements concurrently with the ACE inhibitors may cause hyperkalemia. When the angiotensin II receptor agonists are administered with... 

FIGURE 29-2. Levodopa absorption and metabolism. Levodopa is absorbed in the small intestine and is distributed into the plasma and brain compartments by an active transport mechanism. Levodopa is metabolized by dopa decarboxylase, monoamine oxidase, and catechol-O-methyltransferase. Carbidopa does not cross the blood-brain barrier. Large, neutral amino acids in food compete with levodopa for intestinal absorption (transport across gut endothelium to plasma). They also compete for transport across the brain (plasma compartment to brain compartment). Food and anticholinergics delay gastric emptying resulting in levodopa degradation in the stomach and a decreased amount of levodopa absorbed. If the interaction becomes a problem, administer levodopa 30 minutes before or 60 minutes after meals. 

Although many patients believe that dietary supplements will not interact with medications, recent literature suggests otherwise. Recently, many St. John s wort-drug interactions have been reported in the literature. Cases of patients developing symptoms of serotonin syndrome have been reported with St. John s wort alone and in concomitant therapy with other antidepressants such as monoamine oxidase inhibitors, serotonin reuptake inhibitors, and venlafaxine. St. John s wort may exacerbate the sedative effects of benzodiazepines, alcohol, narcotics, and other sedatives. St. John s wort may decrease the levels of protease inhibitors, cyclosporine, digoxin, and theophylline. 

Inhibition of monoamine oxidase has been proposed as a possible mechanism underlying the hydrogen sulfide-mediated disruption of neurotransmission in brain stem nuclei controlling respiration (Warenycia et al. 1989a). Administration of sodium hydrosulfide, an alkali salt of hydrogen sulfide, has been shown to increase brain catecholamine and serotonin levels in rats. It has also been suggested that persulfide formation resulting from sulfide interaction with tissue cystine and cystinyl peptides may underlie some... 

Phentermine (30 mg in the morning or 8 mg before meals) has less powerful stimulant activity and lower abuse potential than amphetamines and was an effective adjunct in placebo-controlled studies. Adverse effects (e.g., increased blood pressure, palpitations, arrhythmias, mydriasis, altered insulin or oral hypoglycemic requirements) and interactions with monoamine oxidase inhibitors have implications for patient selection. 

AUC, area under the curve, Cmax, maximum concentration MAOI, monoamine oxidase inhibitor TCA, tricyclic antidepressant. Recommended first-line drug interaction search engines Lexi-Comp, Inc Lexi-Comp Online, http //online.lexi.com and Thomson MICROMEDEX Healthcare Series https //www.thomsonhc.com. 

Ottoboni S, Caldera P, Trevor A, et al. Deuterium isotope effect measurements on the interactions of the neurotoxin l-methyl-4-phenyl-l,2,3,6-tetrahydropyridine with monoamine oxidase B. J Biol Chem 1989 264(23) 13684-13688. 

Monoamine Oxidase Inhibitors (MAOIs). Controlled trials comparing the M AOl phenelzine to clomipramine or fluoxetine have produced mixed results. Given the limited data regarding any efficacy of MAOIs in the treatment of OCD coupled with their potentially dangerous interactions, we cannot recommend MAOIs in the treatment of OCD until other approaches have been tried. 

Monoamine Oxidase Inhibitors (MAOIs). Early studies also evaluated the effectiveness of the MAOl phenelzine. Phenelzine, relative to TCAs, provided greater benefit for PTSD however, its usefulness is limited by its potential for drug and food interactions. A recent open label study suggests that the reversible MAOI moclobemide might be helpful for PTSD. It is not available in the United States. 

The first drug-drug interaction alert issued by the Committee in 1966 concerned the risks from interactions between preparations containing adrenaline or noradrenaline and monoamine oxidase (MAO) inhibitors used for the treatment of depression. 

M3. Marley, E., and Blackwell, B., Interactions of monoamine oxidase inhibitors, amines and foodstuffs. Advan. Pharmaml. Chemothtr. 8, 18.5-239 (1970). 

Drugs that may interact with linezolid include monoamine oxidase inhibitors, SSRIs, and adrenergic agents (eg, dopamine, epinephrine). 

Tricyclic antidepressants are notorious for their risk to be involved in drug-drug interactions. Additive anticholinergic effects can be expected in combination with antihistamines, antipsychotics and anticholinergic-type anti-Parkinson agents. Hepatic enzyme-inducing agents increase their hepatic metabolism while enzyme inhibitors may potentiate the effects of tricyclics. Concomitant use with monoamine oxidase inhibitors will produce hypertension, hyperpyrexia and convulsions. 

Brunner D, Buhot MC, Hen R, Hofer M (1999) Anxiety, motor activation, and maternal-infant interactions in 5HT1B knockout mice. Behav Neurosci 113 587-601 Brunner HG, Nelen M, Breakefield XO, Ropers HH, van Oost BA (1993) Abnormal behavior associated with a point mutation in the structural gene for monoamine oxidase A. Science 262 578-580... 

MAOIs work by inhibiting a brain enzyme called monoamine oxidase. Patients taking MAOIs must avoid a substantial list of foods that can interact with the medication and cause dangerously high blood pressure. 

Blackwell, B. (1991) Monoamine oxidase inhibitor interactions with other drugs. / Clin Psychopharmacol 11 55-59. 

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